Linoleic acid is a fatty acid which is effective for the prevention of arteriosclerosis and has an activity of lowering a serum cholesterol level. Linoleic acid is found in the particular species of microorganisms, plants or animals. However, higher animals lack desaturases needed to synthesize linoleic acid so that linoleic acid must be obtained from the diet (vegetable dietary sources).
Linoleic acid is metabolized in vivo to prostaglandins via arachidonic acid. In recent years, intake of a food with a high linoleic acid content such as egg or liver increases. It is pointed out, however, that excessive intake of linoleic acid may imbalance the synthesis of prostaglandins to cause allergic disease, etc.
Pinolenic acid, which is synthesized from linoleic acid, is a Δ5 desaturated fatty acid of 18 carbon atoms having 3 double bonds in one molecule (18:3Δ5,9,12). Since pinolenic acid cannot be metabolized to arachidonic acid in human, it is considered that prostaglandin metabolism is less affected by dietary intake. Also, pinolenic acid has an anticholesteremic activity (see, e.g., Br. J. Nutr., 72, p 775, 1994 [Nonpatent Literature 1]). Based on these findings, dietary oil rich in pinolenic acid, not linoleic acid, is widely marketed as a health food. Besides, fatty acids are used as raw materials to manufacture detergents or biodegradable plastics. Accordingly, pinolenic acid has been a focus of attention also as raw materials for industrial products.
Pinolenic acid is contained in gymnosperms such as pine, etc., and extracted and purified mainly from pine seeds (see, e.g., Eur. J. Lipid Sci. Technol. 104, p 234, 2002 [Nonpatent Literature 2]). However, problems of pine-derived pinolenic acid are pointed out that production costs are high and/or the supply of pines is limited in forest resources, and so on.
Pinolenic acid is considered to be biosynthesized from linoleic acid by the Δ5 desaturation reaction (see, e.g., Nonpatent Literature 2). This reaction is catalyzed by a Δ5 desaturation enzyme (hereinafter abbreviated as “Δ5 desaturase”). Most Δ5 desaturases isolated and identified to date participate in the Δ5 desaturation reaction for converting di-homo-γ-linolenic acid (DGLA, 20:3Δ8,11,14) into arachidonic acid (AA, 20:4Δ5,8,11,14), or eicosatetraenoic acid (ETA, 20:4Δ8,11,14,17) into eicosapentaenoic acid (EPA, 20:4Δ5,8,11,14,17). These enzymes are termed front-end desaturases since they introduce a new double bond at a site most proximal to the carboxyl end than any of the double bonds the substrate fatty acid has (see, e.g., Curr. Opin. Plant Biol. 2, p 123, 1999 [Nonpatent Literature 3]).
Δ5 Desaturase genes that chiefly govern the biosynthesis of polyunsaturated fatty acids having 20 carbon atoms such as AA-EPA, etc. are isolated from filamentous fungi (Mortierella alpina, Pythium irregulare), Thraustochytrium sp., Phaeodactylum tricornutum, Caenorhabditis elegans, rat, human, Physcomitrella patens, Marchantia polymorpha, etc., all of which have the cytochrome b5 domain at the N-terminus (see, e.g., J. Biol. Chem., 273, p 19055, 1998 [Nonpatent Literature 4]), J. Biol. Chem., 273, p 29360, 1998 [Nonpatent Literature 5], Eur. J. Biochem. 269, p 4105, 2002 [Nonpatent Literature 6], FEBS Lett. 439, p 215, 1998 [Nonpatent Literature 7], Arch. Biochem. Biophys., 391, p 8, 2001 [Nonpatent Literature 8], J. Biol. Chem., 274, p 37335, 1999 [Nonpatent Literature 9], J. Biol. Chem., 278, p 35115, 2003 [Nonpatent Literature 10], Plant Mol. Biol., http://ipsapp008.kluweronline.com/IPS/content/ext/x/J/5082/I/124/A/4/type/PDF/article.htm [Nonpatent Literature 11], and J. Biol. Chem. 276, p 31561, 2001 [Nonpatent Literature 12], Lipids, 37, p 863, 2002 [Nonpatent Literature 13], but the sequence of Δ5 desaturase gene for Physcomitrella patens is not published). Also, Δ5 desaturase genes involved in the desaturation of saturated fatty acids or monoenoic acids of 16-20 carbon atoms have been isolated from cellular slime mold Dictyostelium discoideum, Bacillus subtilis, and oil plant meadowfoam (see, e.g., Eur. J. Biochem., 265, 809, 2002 [Nonpatent Literature 14], Eur. J. Biochem., 267, 1813-1818, 2000 [Nonpatent Literature 15], J. Bacteriol., 185, 3228-3231, 2003 [Nonpatent Literature 16], Plant Physiol., 124, 243-251, 2000 [Nonpatent Literature 17]).